<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
        /* 超时调用 间隔一段时间，执行函数，且只执行一次 */
        /* 异步 */
        console.log(1)
        setTimeout(function(){
            console.log("a")
        },2000)
        console.log(2);
    </script>
</body>
</html>